<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<link rel="stylesheet" type="text/css" href="css/lesson3_selectionlevel.css"/>
	</head>
	<body>
		<!--行间样式 > id > class/属性选择器 > div > 通配符选择器-->
		<div id="only" class="demo">123</div>
		<!--<div id="only1">234</div>-->
	</body>
</html>
